This invention relates to semiconductor devices, and particularly to a low-loss diode having a low forward voltage drop and a small reverse leakage current.
The semiconductor rectifying diode is a circuit element for converting AC to DC, and a large number of such diodes are used for electrical equipment powered by DC or for the power supply for electronic equipment. Recently, since most electrical and electronic equipment is now formed by semiconductors, ICs and further LSIs which save energy, the power consumption in the power supply is becoming an important factor which governs the efficiency of the equipment. In order to reduce the power consumption in the power supply, it is necessary to decrease the loss in the semiconductor rectifying diodes which are chief components of the power supply. As one of the methods of decreasing the loss in the semiconductor rectifying diodes, it is known to use the Schottky junction diode in place of the pn junction diode. The Schottky junction diode has a forward voltage drop of as low as 0.5 to 0.6 v, and thus has a low forward loss, but its reverse leakage current is two figures larger than that of the pn junction diode, so that the reverse loss is increased. The total loss of the forward and reverse losses of the Schottky junction diode is only slightly lower than that of the pn junction diode. Thus, the structure of the Schottky junction diode has been improved to decrease the reverse leakage current as disclosed in Japanese Patent Publication Gazette No. 35183/1984, and Japanese Patent Laid-open Gazettes No. 2672/1981, No. 115566/1984 and No. 74582/1985. In these gazettes, semiconductor regions of the opposite conductivity to that of the substrate region are formed to be adjacent to the Schottky junction and to be arranged in parallel with a predetermined spacing so that when a reverse voltage is applied, the pn junction between the semiconductor region and the substrate region is reverse biased. Thus the semiconductor regions are mutually pinched off by the depletion layer spread to the substrate region.
In the Schottky junction diode of the structure in which the current path of the reverse leakage current is pinched off by the depletion layer, it is difficult to reduce the reverse leakage current for the reason which will be described later. Thus, use of the known semiconductor rectifying diodes in the power supply of electric and electronic equipment will increase the loss in the power supply and hence in the equipment. Moreover, a large loss in the power supply results in generation of much heat in the power supply, so that large cooling arrangements become necessary. This prevents the equipment from being small-sized.